Powdery composition of a polymer and a flameproofing agent containing ammonium polyphosphate, method for the production thereof, and moulded body produced from said powder

ABSTRACT

A pulverulent composition that is a powder containing at least one polymer, and at least one flame retardant that contains ammonium polyphosphate, the powder having a maximum particle size of ≦150 μm and a median particle size of from 20 to 100 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Ser. No. 12/332,607,which was filed on Dec. 11, 2008, now U.S. Pat. No. 7,795,339, which acontinuation of U.S. Ser. No. 10/565,779, now abndoned, which was filedon Jan. 25, 2006, which is a National Stage (371) of PCT/EP04/51009,filed on Jun. 3, 2004, and claims priority to DE 1003 33 936.1, filed onJul. 25, 2003, and DE 10 2004 001 324.1, filed on Jan. 8, 2004.

BACKGROUND OF THE INVENTION

The invention relates to a polymer powder which comprises at least onepolymer and at least one flame retardant comprising ammoniumpolyphosphate, to a process for preparing this powder, and also tomoldings produced by layer-by-layer application and fusion of thispowder.

Very recently, a requirement has arisen for the rapid production ofprototypes. The flexibility of processes which apply a pulverulentmaterial layer-by-layer and selectively melt or bond this material makesthese processes of particular interest.

Selective laser sintering is a process particularly well suited to rapidprototyping. In this process, polymer powders in a chamber areselectively irradiated briefly with a laser beam, resulting in meltingof the particles of powder on which the laser beam falls. The moltenparticles coalesce and rapidly solidify again to give a solid mass.Three-dimensional bodies, including those of complex shape, can beproduced simply and rapidly by this process, by repeatedly applyingfresh layers and irradiating these.

The process of laser sintering (rapid prototyping) to realize moldingsmade from pulverulent polymers is described in detail in the patentspecifications U.S. Pat. No. 6,136,948 and WO 96/06881 (both DTMCorporation). A wide variety of polymers and copolymers can be employedfor this application, e.g. polyacetate, polypropylene, polyethylene,ionomers, and polyamide.

Polyamide-12 powder (PA 12) has proven particularly successful inindustry for laser sintering to produce moldings, in particular toproduce engineering components. The parts manufactured from PA 12 powdermeet the high requirements demanded with regard to mechanical loading,and therefore have properties particularly close to those of themass-production parts subsequently produced by extrusion or injectionmolding.

A PA 12 powder with good suitability here has a median particle size(d₅₀) of from 50 to 150 μm, and is obtained as in DE 197 08 946 or elseDE 44 21 454, for example. It is preferable here to use a polyamide-12powder whose melting point is from 185 to 189° C., whose enthalpy offusion is 112±17 J/g, and whose solidification point is from 138 to 143°C., as described in EP 0 911 142.

Other processes with good suitability are the SIB process, as describedin WO 01/38061 or EP 1 015 214. The two processes operate using infraredheating over an area to melt the powder, and selectivity of the meltingis achieved in the first process by applying an inhibitor, and in thesecond process by way of a mask. Another process which has found wideacceptance in the market is 3D printing, as in EP 0 431 924; where themoldings are produced by curing of a binder applied selectively to thepowder layer. Another process is described in DE 103 11 438. In this,the energy required for the fusion process is introduced by way of amicrowave generator, and selectivity is achieved by applying asusceptor.

For the rapid prototyping or rapid manufacturing processes (RP or RMprocesses) mentioned, use may be made of pulverulent substrates, inparticular polymers or copolymers, preferably selected from polyester,polyvinyl chloride, polyacetal, polypropylene, polyethylene,polystyrene, polycarbonate, poly(N-methylmethacrylimides) (PMMI),polymethyl methacrylate (PMMA), ionomer, polyamide, copolyester,copolyamides, terpolymers, acrylonitrile-butadiene-styrene copolymers(ABS), or a mixture of these.

Although the properties of the known polymer powders are already good,moldings produced using these powders still have some disadvantages.Particular disadvantages with the polymer powders currently used aretheir ready flammability and combustibility. This currently inhibits theuse of the abovementioned processes in short production runs, forexample in aircraft construction.

DISCUSSION OF THE INVENTION

It was therefore an object of the present invention to provide a polymerpowder which can give lower flammability of the parts produced therefromby one of the processes described above.

Surprisingly, it has now been found, as described in the claims, thataddition of flame retardants comprising ammonium polyphosphate topolymers or copolymers can make it possible to prepare pulverulentcompositions (powders) from which it is possible to produce moldings bya layer-by-layer process in which regions are selectively melted orbonded to one another, these moldings being markedly less flammable andcombustible than moldings composed of conventional polymer powders.

The present invention therefore provides a pulverulent composition, inparticular a construction powder or rapid-prototyping andrapid-manufacturing powder (RP/RM powder) for rapid-prototyping orrapid-manufacturing applications, for processing in a process for thelayer-by-layer build-up of three-dimensional objects, by selectivelybonding portions of the powder to one another, wherein the powdercomprises at least one polymer and at least one flame retardantcomprising ammonium polyphosphate, the maximum particle size of thepowder being ≦150 μm.

The present invention also provides a process for preparing inventivepowder (pulverulent composition) which comprises preparing a pulverulentmixture in which a polymer and a flame retardant comprising ammoniumpolyphosphate are present.

The present invention also provides the use of inventive powder forproducing moldings by layer-by-layer processes which selectively bondthe powder, and provides moldings produced by a process for thelayer-by-layer build-up of three-dimensional objects, by selectivelybonding portions of a powder to one another, where these comprise atleast one flame retardant comprising ammonium polyphosphate and compriseat least one polymer.

An advantage of the inventive powder is that moldings which have lowercombustibility and flammability can be produced therefrom by an RP or RMprocess as described above for the layer-by-layer build-up ofthree-dimensional objects, portions of the powder used being selectivelybonded to one another. At the same time, the mechanical properties ofthe moldings are substantially retained. This opens up applicationssectors which were inaccessible hitherto because of poor combustibilitygrading. Particularly surprisingly, it is possible to achieve the UL 94(Underwriters Laboratories Inc., test method 94V) classification V-0 forthe finished molding if minimum contents of flame retardant comprisingammonium polyphosphate are maintained within the powders.

Surprisingly, it was also found that moldings produced from theinventive powder have equally good, or even better, mechanicalproperties, in particular increased modulus of elasticity, tensilestrength, and density. The moldings also have good appearance, forexample good dimensional stability and surface quality.

The inventive powder is described below, as also is a process for itspreparation, but there is no intention that the invention be restrictedto these descriptions.

A feature of the inventive construction powder, or of the inventivepulverulent composition for processing in a process for thelayer-by-layer build-up of three-dimensional objects in which portionsof the powder are selectively bonded to one another, is that the powdercomprises at least one polymer and at least one flame retardantcomprising ammonium polyphosphate, and has maximum particle size of ≦150μm, and a median particle size of from 20 to 100 μm. In these processes,the powder is preferably bonded by introducing energy, particularlypreferably by exposure to heat, whereupon the particles are bonded toone another by fusion or sintering. The powder may also be used inprocesses in which the particles are bonded to one another by chemicalreaction or by a binder or by physical measures, preferably drying oradhesion. Details concerning the individual processes may be found inthe abovementioned publications.

The polymer, and also the flame retardant, may be present in theinventive powder in the form of a mixture of the respective powders, orin the form of a powder in which most of the grains, or every grain,comprises not only polymer but also flame retardant. In the case ofthese powders, the distribution of the flame retardant may behomogeneous within the particles, or the concentration of the flameretardant may be greater in the center of the particle or at the surfaceof the particle.

The polymer present in the powder is preferably a homo- or copolymerselected from polyester, polyvinyl chloride, polyacetal, polypropylene,polyethylene, polystyrene, polycarbonate, poly(N-methylmethacrylimides)(PMMI), polymethyl methacrylate (PMMA), ionomer, polyamide, copolyester,copolyamides, terpolymers, acrylonitrile-butadiene-styrene copolymers(ABS), or is a mixture of these. The inventive powder particularlypreferably comprises a polymer which has a melting point of from 50 to350° C., preferably from 70 to 200° C.

The polymers present in the inventive powder may in particular beprepared by milling, precipitation and/or anionic polymerization, or bya combination of these, or by subsequent fractionation.

In particular if the powder is intended to be used for the selectivelaser sintering process, the inventive powder preferably comprises atleast one polyamide. The polyamide present in the inventive powder ispreferably a polyamide which has at least 8 carbon atoms per carboxamidegroup. The inventive powder preferably comprises at least one polyamidewhich contains 9 or more carbon atoms per carboxamide group. The powdervery particularly preferably comprises at least one polyamide selectedfrom polyamide-6,12 (PA 612), polyamide-11 (PA 11) and polyamide-12 (PA12), or copolyamides based on the abovementioned polyamides. Theinventive powder preferably comprises an unregulated polyamide.

A polyamide-12 sinter powder particularly suitable for the lasersintering process is one whose melting point is from 185 to 189° C.,preferably from 186 to 188° C., whose enthalpy of fusion is 112±17 J/g,preferably from 100 to 125 J/g, and whose solidification point is from133 to 148° C., preferably from 139 to 143° C. The preparation processfor the polyamide powders underlying the inventive sinter powders iswell known and, in the case of PA 12, can be found, for example, in thespecifications DE 29 06 647, DE 35 10 687, DE 35 10 691, and DE 44 21454, the content of which is incorporated by way of reference into thedisclosure of the present invention. The polyamide pellets needed can bepurchased from various producers, and by way of example polyamide-12pellets are supplied by Degussa AG under the trade name VESTAMID.

A material which likewise has particularly good suitability ispolyamide-12 whose melting point is from 185 to 189° C., preferably from186 to 188° C., whose enthalpy of fusion is 120±17 J/g, preferably from110 to 130 J/g, and whose solidification point is from 130 to 140° C.,preferably from 135 to 138° C., and whose crystallization point afteraging is also preferably from 135 to 140° C. These test values weredetermined by means of DSC, as described in EP 0 911 142.

A powder which comprises a copolymer, in particular one which is acopolyamide, has particularly good suitability for the processes forproducing three-dimensional objects without use of a laser.

Based on the entirety of polymers present in the powder, the inventivepowder preferably comprises from 5 to 50% by weight of a flame retardantcomprising ammonium polyphosphate, with preference comprises from 10 to40% by weight of a flame retardant comprising ammonium polyphosphate,and particularly preferably comprises from 20 to 35% by weight of aflame retardant comprising ammonium polyphosphate, and very particularlypreferably comprises from 23 to 34% by weight of a flame retardantcomprising ammonium polyphosphate. The ranges given here refer to theentire content of a flame retardant comprising ammonium polyphosphatepresent in the powder, where powder means the entire amount ofcomponents.

The inventive powder may comprise polymer particles mixed with a flameretardant comprising ammonium polyphosphate, or else may comprisepolymer particles or polymer powder which comprise incorporated flameretardant comprising ammonium polyphosphate. If the proportion of aflame retardant comprising ammonium polyphosphate is below 5% by weight,based on the entire amount of components, the desired effect of lowflammability and incombustibility is markedly reduced. If the proportionof a flame retardant comprising ammonium polyphosphate is above 50% byweight, based on the entire amount of components, mechanical properties,such as strain at break, of the moldings produced from these powders aremarkedly impaired.

If the powder comprises polymer particles mixed with a flame retardantcomprising ammonium polyphosphate, the maximum size of the polymerparticles is 150 μm, and their median particle size is preferably from20 to 100 μm, particularly preferably from 45 to 80 μm. The particlesize of the flame retardant comprising ammonium polyphosphate ispreferably below the median grain size d₅₀ of the polymer particles orpolymer powder by at least 20%, preferably by more than 50% and veryparticularly preferably by more than 70%. In particular, the medianparticle size of the flame retardant component is from 1 to 50 μm,preferably from 5 to 15 μm. The small particle size gives gooddispersion of the pulverulent flame retardant within the polymer powder.

The flame retardants present in the inventive powder comprises ammoniumpolyphosphate as principal component. The phosphorus content in theammonium polyphosphate here is preferably from 10 to 35% by weight,preferably from 15 to 32% by weight, and very particularly preferablyfrom 20 to 32% by weight. The flame retardant is preferablyhalogen-free. However, it may comprise synergists, such ascarbon-forming materials, e.g. polyalcohols or pentaerythritol, and/or,by way of example, an intumescent (foaming) component, for examplemelamine. Sulfur may also be present in the composition. If the flameretardant is a powder, it may also comprise a coating, in order toprovide compatibility, or in order to increase the moisture-resistanceof the ammonium polyphosphate. These coated flame retardants areobtainable from Budenheim Iberica under the name Budit, for example.

General commercially available examples of flame retardants comprisingammonium polyphosphate are Budit 3076 DCD or Budit 3076 DCD-2000 fromthe Company Budenheim Iberica, or products from the Exolit AP line, suchas Exolit AP 750 or Exolit AP 422 from the Company Clariant.

In addition, inventive powder may comprise at least one auxiliary, atleast one filler, and/or at least one pigment. By way of example, theseauxiliaries may be flow aids, e.g. fumed silicon dioxide, or elseprecipitated silicic acid. Fumed silicon dioxide (fumed silicic acid) issupplied by Degussa AG under the product name Aerosil® with variousspecifications, for example. In particular, the flow aids may behydrophobic flow aids. Inventive powder preferably comprises less than3% by weight, with preference from 0.001 to 2% by weight, and veryparticularly preferably from 0.05 to 1% by weight, of these auxiliaries,based on the entirety of components, i.e. on the entirety of polymersand flame retardant. By way of example, the fillers may be glassparticles, metal particles, in particular aluminum particles, or ceramicparticles, e.g. solid or hollow glass beads, steel shot, aluminumspheres, or granulated metal, or else color pigments, e.g. transitionmetal oxides.

The median grain size of the filler particles here is preferably smallerthan, or approximately equal to, that of the particles of the polymers.The extent to which the median grain size d₅₀ of the fillers exceeds themedian grain size d₅₀ of the polymers should preferably be not more than20%, with preference not more than 15%, and very particularly preferablynot more than 5%. A particular limit on the particle size arises via thepermissible overall height or layer thickness in the particularapparatus used for the layer-by-layer process.

Inventive powder preferably comprises less than 70% by weight, withpreference from 0.001 to 60% by weight, particularly preferably from0.05 to 50% by weight, and very particularly preferably from 0.5 to 25%by weight, of these fillers, based on the entirety of components, suchthat the proportion by volume of the polymers is always greater than50%.

If the stated maximum limits for auxiliaries and/or fillers areexceeded, depending on the filler or auxiliary used, the result can bemarked impairment of the mechanical properties of moldings producedusing these powders.

The inventive powders may be prepared in a simple manner, preferably bythe inventive process for preparing inventive powder, by mixing at leastone polymer with at least one flame retardant comprising ammoniumpolyphosphate. The dry blend mixing process may be used for dry mixing.In a preferred method, a polymer powder obtained, by way of example, byreprecipitation and/or milling, which may also subsequently befractionated, is mixed with the flame retardant comprising ammoniumpolyphosphate. It can be advantageous here to provide a flow aidinitially to the pulverulent flame retardant alone, or else to thefinished mixture, for example one from the Aerosil R line from Degussa,e.g. Aerosil R972 or R812. In another variant of the process, the flameretardant comprising ammonium polyphosphate may be compounded into amelt of at least one polymer, and the resultant mixture may be processedby milling to give powder. The processing of ammoniumpolyphosphate-based flame retardants in the compounding is described byway of example in Plastics Additives & Compounding, April 2002, ElsevierAdvanced Technology, pp. 28 to 33.

In the simplest embodiment of the inventive process, by way of example,fine-particle mixing may take place by a mixing process which appliesfinely pulverized flame retardant to the dry powder in high-speedmechanical mixers.

In one of these first variants of the inventive process, the powder maybe a polymer powder which is itself suitable for the layer-by-layerrapid prototyping process, fine particles of the flame retardant simplybeing admixed with this powder. The median grain size of the particleshere is preferably smaller than, or at most approximately equal to, thatof the particles of the polymers. The extent to which the median grainsize d₅₀ of the flame retardant particles is less than the median grainsize d₅₀ of the polymer powders should preferably be more than 20%, withpreference more than 50%, and very particularly preferably more than70%. A particular upward limit on the grain size arises via thepermissible overall height or layer thickness in the rapid prototypingsystem.

It is also possible to mix conventional polymer powders with inventivepowders. This method can prepare powders with an optimal combination ofmechanical and flame-retardant properties. By way of example, theprocess for preparing mixtures of this type may be found in DE 34 41708.

In another variant of the process, the flame retardant is mixed with a,preferably molten, polymer via incorporation by compounding, and theresultant polymer comprising flame retardant is processed by (lowtemperature) milling and, where appropriate, fractionation to giveinventive powder. The compounding generally gives pellets which are thenprocessed to give powder. An example of a method for this conversionprocess is milling. The process variant in which the flame retardant isincorporated by compounding has the advantage over the pure mixingprocess of giving more homogeneous distribution of the flame retardantwithin the powder.

Where appropriate, a suitable flow aid, such as fumed aluminum oxide,fumed silicon dioxide, or fumed titanium dioxide, may be addedexternally to the precipitated or low-temperature-milled powder, inorder to improve flow performance.

A flow-control agent, such a metal soaps, preferably the alkali metal oralkaline earth metal salts of the underlying alkanemonocarboxylic acidsor dimer acids, may be added to the precipitated orlow-temperature-milled powder in order to improve melt flow during theproduction of the moldings.

Flame retardants that may be used are commercially available products,for example those which may be purchased from Budenheim Iberica orClariant under the trade name Exolit AP® or Budit®, or those describedabove.

The amounts used of the metal soaps are from 0.01 to 30% by weight,preferably from 0.5 to 15% by weight, based on the entirety ofpolyamides present in the powder. Metal soaps preferably used are thesodium or calcium salts of the underlying alkanemonocarboxylic acids ordimer acids. Examples of commercially available products are LicomontNaV or Licomont CaV from Clariant.

The metal soap particles may be incorporated into the polyamideparticles, or else fine metal soap particles may have been mixed withpolyamide particles.

In order to improve processability, or for further modification of thepowder, this may treated with inorganic pigments, in particular colorpigments, e.g. transition metal oxides, stabilizers, e.g. phenols, inparticular sterically hindered phenols, flow control agents and flowaids, e.g. fumed silicic acids, and also filler particles. Based on thetotal weight of components in the powder, the amount of these substancesadded to the powder is preferably such as to comply with the statedconcentrations for fillers and/or auxiliaries for the inventive powder.

The present invention also provides the use of inventive powder forproducing moldings in a layer-by-layer process which selectively bondsthe powder (rapid prototyping or rapid manufacturing), these beingprocesses which use inventive powders, the polymers, and a flameretardant comprising ammonium polyphosphate, preferably each inparticulate form.

The present invention in particular provides the use of the powder forproducing moldings via selective laser sintering of a precipitationpowder comprising flame retardant and based on a polyamide-12 which hasa melting point of from 185 to 189° C., and enthalpy of fusion of 112±17J/g, and a solidification point of from 136 to 145° C., and the use ofwhich is described in U.S. Pat. No. 6,245,281.

Laser sintering processes are sufficiently well known, and are based onthe selective sintering of polymer particles, where layers of polymerparticles are briefly exposed to laser light and the polymer particlesexposed to the laser light are thus bonded to one another. Successivesintering of layers of polymer particles produces three-dimensionalobjects. Details concerning the selective laser sintering process arefound, by way of example, in the specifications U.S. Pat. No. 6,136,948and WO 96/06881. However, the inventive powder may also be used in otherrapid prototyping or rapid manufacturing processing of the prior art, inparticular in those described above. For example, the inventive powdermay in particular be used for producing moldings from powders via theSLS (selective laser sintering) process, as described in U.S. Pat. No.6,136,948 or WO 96/06881, via the SIB process (selective inhibition ofbonding of powder), as described in WO 01/38061, via 3D printing, asdescribed in EP 0 431 924, or via a microwave process, as described inDE 103 11 438. The specifications cited, and in particular the processesdescribed therein, are expressly incorporated into the disclosurecontent of the present description of the invention by way of reference.

Careful handling of the inventive powders is advisable because the flameretardants are air-sensitive. In particular, prolonged contact of theinventive powder with air or with atmospheric moisture is to be avoided.The sensitivity of the inventive powder can be reduced by usinghydrophobic flow aids, thus permitting avoidance of any reduction inmodulus of elasticity which is sometimes caused by the decompositionproducts of ammonium polyphosphate.

The inventive moldings, produced via a process for the layer-by-layerbuild-up of three-dimensional objects, in which portions of a powder, inparticular of the inventive powder, are selectively bonded to oneanother, e.g. selective laser sintering, comprise at least one flameretardant comprising ammonium polyphosphate and comprise at least onepolymer, or are composed of at least one flame retardant comprisingammonium polyphosphate and of at least one polymer. The inventivemoldings preferably comprise at least one polyamide which contains atleast 8 carbon atoms per carboxamide group. Inventive moldings veryparticularly preferably comprise at least one polyamide-6,12,polyamide-11 and/or one polyamide-12, or copolyamides based on thesepolyamides, and comprise at least one flame retardant comprisingammonium polyphosphate.

The flame retardant present in the inventive molding is based onammonium polyphosphate. The inventive molding preferably comprises,based on the entirety of components present in the molding, from 5 to50% by weight of flame retardant comprising ammonium polyphosphate,preferably from 10 to 40% by weight, particularly preferably from 20 to35% by weight, and very particularly preferably from 23 to 24% byweight. The proportion of flame retardant comprising ammoniumpolyphosphate is preferably at most 50% by weight, based on the entiretyof components present in the molding. Based on the entirety of polymerspresent, the molding comprises from 30 to 35% by weight of flameretardant comprising ammonium polyphosphate.

Besides polymer and flame retardant, the moldings may also comprisefillers and/or auxiliaries, and/or pigments, e.g. heat stabilizersand/or antioxidants, e.g. sterically hindered phenol derivatives.Examples of fillers may be glass particles, ceramic particles, or elsemetal particles, e.g. iron shot, or corresponding hollow spheres. Theinventive moldings preferably comprise glass particles, veryparticularly preferably glass beads. Inventive moldings preferablycomprise less than 3% by weight, with preference from 0.001 to 2% byweight, and very particularly preferably from 0.05 to 1% by weight, ofthese auxiliaries, based on the entirety of components present.Inventive moldings likewise preferably comprise less than 75% by weight,with preference from 0.001 to 70% by weight, particularly preferablyfrom 0.05 to 50% by weight, and very particularly preferably from 0.5 to25% by weight, of theses fillers, based on the entirety of componentspresent.

EXAMPLES

The examples below are intended to describe the inventive pulverulentcomposition, and also its use, without restricting the invention to theexamples.

The method used in the following examples for BET surface areadetermination complied with DIN 66 131. Bulk density was determinedusing an apparatus to DIN 53 466. A Malvern Mastersizer S, version 2.18,was used to obtain the laser scattering values.

Example 1 Comparative Example (Non-Inventive)

40 kg of unregulated PA 12 prepared by hydrolytic polymerization by amethod based on DE 35 10 691, example 1, and having a relative solutionviscosity η_(rel) of 1.61 (in acidified m-cresol) and having anend-group content of 72 mmol/kg of COOH and, respectively, 68 mmol/kg ofNH₂ are heated to 145° C. within a period of 5 hours in 0.8 m³ stirredtank (D=90 cm, h=170 cm) with 0.3 kg of IRGANOX® 1098 in 350 l ofethanol, denatured with 2-butanone and 1% water content, and held atthis temperature for 1 hour, with stirring (blade stirrer, d=42 cm,rotation rate=91 rpm). The jacket temperature is then reduced to 120°C., and the internal temperature is brought to 120° C. at a cooling rateof 45 K/h, using the same stirrer rotation rate. From this junctureonward, the jacket temperature is held at from 2 to 3 K below theinternal temperature, using the same cooling rate. The internaltemperature is brought to 117° C., using the same cooling rate, and thenheld constant for 60 minutes. The internal temperature is then broughtto 111° C., using a cooling rate of 40 K/h. At this temperature theprecipitation begins and is detectable via evolution of heat. After 25minutes the internal temperature falls, indicating the end of theprecipitation. After cooling of the suspension to 75° C., the suspensionis transferred to a paddle dryer. The ethanol is distilled off from thematerial at 70° C. and 400 mbar, with stirring, and the residue is thenfurther dried at 20 mbar and 85° C. for 3 hours.

-   BET: 6.9 m²/g-   Bulk density: 429 g/l-   Laser scattering: d(10%): 42 μm, d(50%): 69 μm, d(90%): 91 μm

Example 2 Incorporation of Budit 3076 DCD Via Compounding Followed byMilling

40 kg of unregulated PA 12, of the type represented by Vestamid L1600from Degussa AG, and prepared by hydrolytic polymerization are extrudedwith 0.3 kg of IRGANOX® 245 and 12 kg (30 parts) of flame retardant(Budit 3076 DCD, Budenheim Iberica) at 220° C. in a twin-screwcompounding machine (Bersttorf ZE25), and strand-pelletized. The pelletsare then milled at low temperatures (−40° C.) in an impact mill to givea grain size distribution from 0 to 120 μm. 40 g of Aerosil 200 (0.1part) are then mixed into the material at room temperature and 500 rpmfor 3 minutes.

Example 3 Incorporation of Budit 3076 DCD-2000 in a Dry Blend Process

1023 g (35 parts) of Budit 3076 DCD-2000 are mixed within a period of 3minutes with 1900 g (65 parts) of polyamide-12 powder, prepared as in DE29 06 647, example 1, and having a median grain diameter d₅₀ of 56 μm(laser scattering) and a bulk density of 459 g/l to DIN 53 466, in a dryblend process utilizing a FML10/KM23 Henschel mixer at 700 rpm and at50° C. 1.5 g of Aerosil R 812 (0.05 part) were then mixed into thematerial within a period of 3 minutes at room temperature and 500 rpm.

Other powders comprising 10, 20, 25, 30 and 35 parts of Budit 3076DCD-2000 flame retardant were prepared under the same conditions.

Example 4 Incorporation of Budit 3076 DCD and Metal Soap in a Dry BlendProcess

814 g (30 parts) of Budit 3076 DCD are mixed within a period of 3minutes with 1900 g (70 parts) of polyamide-12 powder, prepared as in DE29 06 647, example 1, and having a median grain diameter d₅₀ of 56 μm(laser scattering) and a bulk density of 459 g/l to DIN 53 466, in a dryblend process utilizing a FML10/KM23 Henschel mixer at 700 rpm and at50° C. 54 g (2 parts) of Licomont NaV and 2 g of Aerosil 200 (0.1 part)were then mixed into the material within a period of 3 minutes at roomtemperature and 500 rpm.

Example 5 Incorporation of Exolit AP 422 in a Dry Blend Process

475 g (20 parts) of Exolit AP 422 are mixed within a period of 3 minuteswith 1900 g (80 parts) of polyamide-12 powder, prepared as in DE 29 06647, example 1, and having a median grain diameter d₅₀ of 56 μm (laserscattering) and a bulk density of 459 g/l to DIN 53 466, in a dry blendprocess utilizing a FML10/KM23 Henschel mixer at 700 rpm and at 50° C.2.4 g of Aerosil R 200 (0.1 part) were then mixed into the materialwithin a period of 3 minutes at room temperature and 500 rpm.

Other powders comprising 10, 25, 30 and 35 parts of Exolit AP 422 flameretardant were prepared under the same conditions.

Further Processing and Testing

The powders from examples 1 to 4 were used in a laser sintering machineto build up bars for the UL 94V fire-protection test, and also to buildup multipurpose bars to ISO 3167. The latter components were used todetermine mechanical properties by means of a tensile test to EN ISO 527(table 1). The UL bars were used for the vertical UL 94V (UnderwritersLaboratories Inc.) combustion test. The bars have specified dimensionsof 3.2*10*80 mm. Each was produced on an EOSINT P360 laser sinteringmachine from EOS GmbH.

TABLE 1 Test results from the samples of examples 1 to 3 Test barModulus of Total UL thickness elasticity burning UL Examples [mm] N/mm²time [s] classification Molding composed of material from 3.9 1688 >167none example 1 Molding composed of material from 3.6 1890 19 V-0 example2 Molding composed of material from 3.6 1860 11 V-0 example 4, 30% ofBudit 3076 DCD-2000 Molding composed of material from 3.6 1885 10 V-0example 3, 30% of Budit 3076 DCD-2000 Molding composed of material from3.6 2031 9 V-0 example 3, 35% of Budit 3076 DCD-2000 Molding composed ofmaterial from 3.7 2313 10 V-0 example 5, 30% of Exolit AP 422 Moldingcomposed of material from 3.7 2207 10 V-0 example 5, 20% of Exolit AP422(none: no classification into any of the grades V-0 to V-2 was possible.The bars are thicker than the specified thickness, this beingattributable firstly to the z compensation (the laser beam reaches morethan one layer thickness since, of course, it also has to reach thelayer boundary, but this is more than required for the first layer), andsecondly to the slightly intumescent (foaming) action of some flameretardants.

It can clearly be seen that the addition of flame retardant based onammonium polyphosphate to the polymer powder can produce moldings whoseUL classification is markedly better. The addition of the flameretardant moreover increases the modulus of elasticity and the tensilestrength, but there is a simultaneous reduction in the elongation atbreak.

What we claim is:
 1. A pulverulent composition, wherein the pulverulentcomposition is a powder comprising: at least one polymer, and at leastone flame retardant that comprises ammonium polyphosphate wherein thepowder has a maximum particle size of ≦150 μm and wherein the powder hasa median particle size of from 20 to 100 μm, wherein the at least onepolymer is at least a polyamide.
 2. The pulverulent composition asclaimed in claim 1, wherein the polymer is prepared by at least one ofmilling, precipitation, anionic polymerization, or by a combination ofthese, or by subsequent fractionation.
 3. The pulverulent composition asclaimed in claim 1, wherein said powder further comprises at least onepolymer selected from the group consisting of polyester, polyvinylchloride, polyacetal, polypropylene, polyethylene, polystyrene,polycarbonate, poly-(N-methylmethacrylimides) (PMMI), polymethylmethacrylate (PMMA), ionomer, copolyester, terpolymers, andacrylonitrile-butadiene-styrene copolymers (ABS), or a copolymercomprising at least two polymers selected from the group consisting ofpolyester, polyvinyl chloride, polyacetal, polypropylene, polyethylene,polystyrene, polycarbonate, poly-(N-methylmethacrylimides) (PMMI),polymethyl methacrylate (PMMA), ionomer, copolyester, terpolymers, andacrylonitrile-butadiene-styrene copolymers (ABS).
 4. The pulverulentcomposition as claimed in claim 1, wherein the polymer ispolyamide-6,12, polyamide-11, polyamide-12, or a copolymer of thesepolyamides.
 5. The pulverulent composition as claimed in claim 1,wherein the polymer has a melting point of from 50 to 350° C.
 6. Thepulverulent composition as claimed in claim 5, wherein the polymer has amelting point of from 70 to 200° C.
 7. The pulverulent composition asclaimed in claim 1, further comprising at least one auxiliary, filler,or pigment.
 8. The pulverulent composition as claimed in claim 7, whichcomprises a flow aid as an auxiliary.
 9. The pulverulent composition asclaimed in claim 1, wherein the ammonium polyphosphate contains from 10to 35% by weight of phosphorus.
 10. The pulverulent composition asclaimed in claim 1, wherein the flame retardant component comprises asynergist with the ammonium polyphosphate.
 11. The pulverulentcomposition as claimed in claim 1, wherein the flame retardant componentis in a pulverulent form with a median particle size of from 1 to 50 μm.12. The pulverulent composition as claimed in claim 1, wherein the flameretardant component is in a pulverulent and a coated form.
 13. A methodfor producing moldings by a layer-by-layer process which selectivelybonds the powder, the method comprising: adding the pulverulentcomposition of claim 1 to a molding mixture.
 14. The method of claim 13,wherein the moldings are produced by selective laser sintering,selective inhibition of the bonding of powders, 3D printing, or amicrowave process.
 15. A molding, produced by a process for thelayer-by-layer build-up of three-dimensional objects by selectivelybonding portions of a powder to one another, the molding comprising: atleast one flame retardant that comprises ammonium polyphosphate, and atleast one polymer, wherein the powder has a maximum particle size of≦150 μm and wherein the powder has a median particle size of from 20 to100 μm, wherein the at least one polymer is at least a polyamide. 16.The molding as claimed in claim 15, wherein said polyamide contains atleast 8 carbon atoms per carboxamide group.
 17. The molding as claimedin claim 15, wherein the polymer is polyamide-6,12, polyamide-11,polyamide-12, or a copolymer of these polyamides.
 18. The molding asclaimed in claim 15, wherein the flame retardant is present in an amountof from 5 to 50% by weight, based on the total amount of componentspresent, and wherein the flame retardant comprises ammoniumpolyphosphate.
 19. The molding as claimed in claim 15, which, whereinthe flame retardant is present in an amount of from 30 to 35% by weight,based on the total amount of the polymers present, and wherein the flameretardant comprises ammonium polyphosphate.
 20. The molding as claimedin claim 15, further comprising fillers and/or pigments.